At this price, these prebuilt tablets are much cheaper than attempting to build something from the ground up(as with BeagleBoard which admitedly runs a much more powerful CPU)
There's a photo of it running debian here, and some details for running debian on another device with the same SoC architecture (WM8505): http://slatedroid.com/index.php?topic=152.0
The easy way is undoubtedly to use debootstrap and keep the current kernel it's running. I think that's more or less an easy and given possibility, because once you have the serial port connected you have a root console (or presumably you can unlock root access in software via Android.)
Building a kernel as well may be harder. From what I can tell, and it's hard to tell because most people (including Eken) aren't releasing source at the moment (sigh), this may be hard because of a bunch of proprietary M8505 modules in the current kernel. Not sure yet, though.
The M001 is $99 including shipping anywhere in the world.
IIRC, 2.2 will at minimum require someone to build a newer kernel, which AFAIK noone has worked out how to do (see my post above about proprietary WM8505 modules.)
It's hard for a noob like me to work it all out though, because almost noone is releasing any source or doing their development work in public (I intend to post anything useful that I figure out.)
I was thinking about trying it myself, but I mostly bought it to put debian on it, and remove the board to use it as a robot controller. Not to mention that the Android build process looks tricky and extremely device-specific, from what I've seen :).